1. Field of the Invention
The present invention relates to an engine control apparatus and more particularly to an engine control apparatus which changes the engine combustion mode and performs fuel injection plural times for each cylinder combustion.
2. Description of the Related Art
As an internal combustion engine subjected to engine combustion mode changeover control, a spark internal combustion engine which injects fuel into the combustion chamber disclosed in, for example, JP-A-2005-155498 is known. With the spark internal combustion engine, not only an injection stroke for setting the fuel injection timing but also the ignition timing is changed in relation to its starting state. Upon ignition timing changeover, the ignition timing for the injection stroke after changeover is selected through an intermediate operation period of the internal combustion engine based on an intermediate ignition timing between an ignition timing for an injection stroke before changeover and an ignition timing for an injection stroke after changeover. Specifically, the fuel injection timing is changed in relation to each combustion stroke of the engine to attain different combustion modes.
The technique disclosed in JP-A-2005-155498 restrains the level difference in the output torque of the internal combustion engine taking into consideration the ignition timing upon injection stroke changeover. As a prerequisite, the fuel injection timing is set in the compression stroke for catalyst warm-up after the internal combustion engine is started up and the ignition timing is largely retarded.